/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression;

import org.springframework.lang.Nullable;

/**
 * PropertyAccessor属性访问器是SpEL中一个非常重要的概念。它内置的实现也有多种：
 * <p>
 * 这个接口返回的类型相当于告诉SpEL它能够处理的targetType类型，若返回null，表示它通处理所有的type
 *
 * @author Andy Clement
 * @since 3.0
 */
public interface PropertyAccessor {

	/**
	 * Return an array of classes for which this resolver should be called.
	 * <p>Returning {@code null} indicates this is a general resolver that
	 * can be called in an attempt to resolve a property on any type.
	 *
	 * @return an array of classes that this resolver is suitable for
	 * (or {@code null} if a general resolver)
	 */
	@Nullable
	Class<?>[] getSpecificTargetClasses( );

	/**
	 * Called to determine if a resolver instance is able to access a specified property
	 * on a specified target object.
	 *
	 * @param context the evaluation context in which the access is being attempted
	 * @param target  the target object upon which the property is being accessed
	 * @param name    the name of the property being accessed
	 * @return true if this resolver is able to read the property
	 * @throws AccessException if there is any problem determining whether the property can be read
	 */
	boolean canRead(EvaluationContext context, @Nullable Object target, String name) throws AccessException;

	/**
	 * Called to read a property from a specified target object.
	 * Should only succeed if {@link #canRead} also returns {@code true}.
	 *
	 * @param context the evaluation context in which the access is being attempted
	 * @param target  the target object upon which the property is being accessed
	 * @param name    the name of the property being accessed
	 * @return a TypedValue object wrapping the property value read and a type descriptor for it
	 * @throws AccessException if there is any problem accessing the property value
	 */
	TypedValue read(EvaluationContext context, @Nullable Object target, String name) throws AccessException;

	/**
	 * Called to determine if a resolver instance is able to write to a specified
	 * property on a specified target object.
	 *
	 * @param context the evaluation context in which the access is being attempted
	 * @param target  the target object upon which the property is being accessed
	 * @param name    the name of the property being accessed
	 * @return true if this resolver is able to write to the property
	 * @throws AccessException if there is any problem determining whether the
	 *                         property can be written to
	 */
	boolean canWrite(EvaluationContext context, @Nullable Object target, String name) throws AccessException;

	/**
	 * Called to write to a property on a specified target object.
	 * Should only succeed if {@link #canWrite} also returns {@code true}.
	 *
	 * @param context  the evaluation context in which the access is being attempted
	 * @param target   the target object upon which the property is being accessed
	 * @param name     the name of the property being accessed
	 * @param newValue the new value for the property
	 * @throws AccessException if there is any problem writing to the property value
	 */
	void write(EvaluationContext context, @Nullable Object target, String name, @Nullable Object newValue)
			throws AccessException;

}
